1. Field of the Invention
The invention relates generally to sheet feeding, separating and transporting apparatus and more particularly to bottom loading sheet feeders adapted for use in conjunction with continuous flow automated document processing systems.
2. Description of the Prior Art
Sheet feeding apparatus have provided sheet removal and transfer from a stack of sheets lying in either horizontal or vertical planes. Generally, these sheet feeders were adapted to separate in seriatim a batch of sheets with the feed stack or bundle constituting the batch. Depletion of the batch necessitated reloading the feeder magazine and usually implied interruption of feeder operation. The reloading function has generally been performed manually even with information storage and retrieval system feeders.
While it may have been possible to automatically or manually resupply a depleting stack carried in a magazine above a bottom-of-stack sheet feeder, various disadvantages have been encountered with respect to bottom-of-stack feeders when attempts were made to utilize such feeders for continuous high speed delivery and transport of sheets. Poor reliability has been encountered with such feeders primarily due to their sensitivity to variable stack pressures and concomitant variations in intersheet friction.
Sheet feeders designed for separating and transporting stacks of sheets oriented edgewise, i.e. in vertical planes, were primarily designed for utilization in instances where the sheets were substantially self-supporting in such vertical planes, e.g. envelopes, cards, checks, etc., and such feeders have thus been found to be impractical for utilization where letter size papers are to be separated from a stack.
Top-of-stack sheet feeding mechanisms generally separated the top sheet through a shingling process which often employed a reverse drive wheel to retard double feeding. While such systems were practical in instances wherein the sheets had reasonable stiffness, e.g. envelopes, cards, etc., they too could not be reliably employed to feed single sheets of paper.
Most prior feeders utilized a variable force for engaging the stack against a feed roller. In some instances a spring loader applied pressure to the end of the stack, while in others the feeder itself was biased to dip into the stack as the stack was being depleted. These prior devices permitted variations in stack pressure which affected feeder reliability and versatility.